1. Field of the Invention
This invention relates generally to deformable mirrors for an adaptive optics system, and in particular to coupling the deformable mirror to receive electric potential for causing deformations in the mirror.
2. Background of the Invention
There is an increasing interest in the use of free-space optical communications for various applications. For example, much of the current telecommunications infrastructure is based on the transmission of optical signals via optical fibers. While the use of fiber optics has increased the capacity and efficiency of data transmission, there are many situations where the installation of new fiber is not the best solution. As a result, there is interest in augmenting the telecommunications infrastructure by transmitting optical signals through the free-space of the atmosphere.
Free-space optical communications links can also be used advantageously in applications outside of the telecommunications infrastructure. Compared to other communications technologies, a free-space optical communications link can have advantages of higher mobility and compact size, better directionality (e.g., harder to intercept), faster set up and tear down, and/or suitability for situations where one or both transceivers are moving. Thus, free-space optical communications links can be used in many different scenarios, including in airborne, sea-based, space and/or terrestrial situations.
However, in many of these potential applications, the free-space optical communications link suffers from optical aberrations. For example, changes in atmospheric conditions can be a significant impediment to the accuracy, reliability and efficiency of free-space optical communications systems. Wind, heat waves, man-made pollutants and other effects can create constantly changing aberrations. This, in turn, can degrade the quality of the optical signal that is available at the receiver, resulting in degradation of the overall quality and efficiency of the communications channel.
To address the problem of optical aberrations, adaptive optics systems have been developed to compensate for these aberrations, thus improving the performance of free space optical communications systems. In addition to free-space optical communications, adaptive optics systems can be applied in other areas where optical aberrations are also problematic, such as for telescopes.
Some adaptive optics systems include a wavefront sensor, which senses the aberrations in the wavefront of light waves and provides a signal for correcting or compensating for those aberrations. Existing methods and devices for sensing and measuring the wavefront include several interferometric techniques, the Shack-Hartmann wavefront sensing techniques and various other systems that involve the projection of patterns of light through an optical system. Once the wavefront senor has measured these aberrations, it can provide a signal to a device for correcting the aberrations, such as a deformable mirror. By adaptively deforming to compensate for the measured aberrations in the light waves, the optical system can correct for these aberrations.
But these techniques and systems are typically complex and expensive and have various inherent deficiencies. In addition to the deficiencies of existing wavefront sensors, the deformable mirrors that are controlled by those wavefront sensors also have a number of deficiencies. One type of deformable mirror used is a stack actuator mirror. A stack actuator mirror include a number of push rods that engage the back of a flexible mirror so that the extension and retraction of each push rod causes an associated deformation in the mirror. These rods are controlled by the wavefront sensor, which effectively controls the deformation of the mirror.
The Shack-Hartman wavefront sensor measures local slopes of various points across a wavefront, and these slopes are provided to a wavefront reconstructor. The wavefront reconstructor matches the measured slopes to generate a continuous surface for the reconstructed wavefront. This type fitting is blind to hysterisis effects in the actuators, thereby causing a waffle pattern to appear on the mirror surface. Because the push rods tend to produce a deformation in the mirror that is nearly a straight line on the mirror surface between each pair of adjacent push rods, the push rods may do a poor job deforming the mirror in a curved pattern generated by the wavefront reconstructor, especially when a small number of actuators are used. Moreover, the number of push rods, the closeness of the push rods, and the length of their travel are physically limited. Since all actuators have the same travel and are attached to a rigid reference surface, the mirror has the same stroke for all modes (i.e., low order focus has the same stroke as the highest mode produced by every other actuator being turned on and off.) For correcting the aberrations originating in the atmosphere, this range of stroke at the highest modes is not necessary, and the corrections may not be accurate for small errors. Accordingly, the accuracy and degree of optical correction that can be applied by the stack actuator type mirror is limited.
One deformable mirror that overcomes many of these problems uses an electro-restrictive or piezoelectric material to deform the mirror in a controllable manner. Voltages are selectively applied to electrodes to deform the mirror. Connections to the individual electrodes are made by manually soldering wires to each electrode from. The wires couple the electrode to a printed circuit board, which provides voltages to the electrode for deforming the mirror. This method is difficult and time consuming, however, and can take hours to make the connections for a single mirror. Further, the connections can distort the mirror, the connected wires add mass to the mirror and therefore lower the resonant frequency of the mirror, and it is difficult to mass-produce wired mirrors using this method. Moreover, conductors carrying electricity in the same layer as the electrodes can cause an electric field that deforms the mirror in undesirable ways. Therefore, it is desirable to provide a better method for connecting the electrodes of the deformable mirror.